1# $OpenBSD: leap-seconds.list,v 1.5 2025/01/19 22:03:27 millert Exp $ 2# ATOMIC TIME 3# Coordinated Universal Time (UTC) is the reference time scale derived 4# from The "Temps Atomique International" (TAI) calculated by the Bureau 5# International des Poids et Mesures (BIPM) using a worldwide network of atomic 6# clocks. UTC differs from TAI by an integer number of seconds; it is the basis 7# of all activities in the world. 8# 9# 10# ASTRONOMICAL TIME (UT1) is the time scale based on the rate of rotation of the earth. 11# It is now mainly derived from Very Long Baseline Interferometry (VLBI). The various 12# irregular fluctuations progressively detected in the rotation rate of the Earth led 13# in 1972 to the replacement of UT1 by UTC as the reference time scale. 14# 15# 16# LEAP SECOND 17# Atomic clocks are more stable than the rate of the earth's rotation since the latter 18# undergoes a full range of geophysical perturbations at various time scales: lunisolar 19# and core-mantle torques, atmospheric and oceanic effects, etc. 20# Leap seconds are needed to keep the two time scales in agreement, i.e. UT1-UTC smaller 21# than 0.9 seconds. Therefore, when necessary a "leap second" is applied to UTC. 22# Since the adoption of this system in 1972 it has been necessary to add a number of seconds to UTC, 23# firstly due to the initial choice of the value of the second (1/86400 mean solar day of 24# the year 1820) and secondly to the general slowing down of the Earth's rotation. It is 25# theoretically possible to have a negative leap second (a second removed from UTC), but so far, 26# all leap seconds have been positive (a second has been added to UTC). Based on what we know about 27# the earth's rotation, it is unlikely that we will ever have a negative leap second. 28# 29# 30# HISTORY 31# The first leap second was added on June 30, 1972. Until the year 2000, it was necessary in average to add a 32# leap second at a rate of 1 to 2 years. Since the year 2000 leap seconds are introduced with an 33# average interval of 3 to 4 years due to the acceleration of the Earth's rotation speed. 34# 35# 36# RESPONSIBILITY OF THE DECISION TO INTRODUCE A LEAP SECOND IN UTC 37# The decision to introduce a leap second in UTC is the responsibility of the Earth Orientation Center of 38# the International Earth Rotation and reference System Service (IERS). This center is located at Paris 39# Observatory. According to international agreements, leap seconds should be scheduled only for certain dates: 40# first preference is given to the end of December and June, and second preference at the end of March 41# and September. Since the introduction of leap seconds in 1972, only dates in June and December were used. 42# 43# Questions or comments to: 44# Christian Bizouard: christian.bizouard@obspm.fr 45# Earth orientation Center of the IERS 46# Paris Observatory, France 47# 48# 49# 50# COPYRIGHT STATUS OF THIS FILE 51# This file is in the public domain. 52# 53# 54# VALIDITY OF THE FILE 55# It is important to express the validity of the file. These next two dates are 56# given in units of seconds since 1900.0. 57# 58# 1) Last update of the file. 59# 60# Updated through IERS Bulletin C (https://hpiers.obspm.fr/iers/bul/bulc/bulletinc.dat) 61# 62# The following line shows the last update of this file in NTP timestamp: 63# 64#$ 3945196800 65# 66# 2) Expiration date of the file given on a semi-annual basis: last June or last December 67# 68# File expires on 28 December 2025 69# 70# Expire date in NTP timestamp: 71# 72#@ 3975868800 73# 74# 75# LIST OF LEAP SECONDS 76# NTP timestamp (X parameter) is the number of seconds since 1900.0 77# 78# MJD: The Modified Julian Day number. MJD = X/86400 + 15020 79# 80# DTAI: The difference DTAI= TAI-UTC in units of seconds 81# It is the quantity to add to UTC to get the time in TAI 82# 83# Day Month Year : epoch in clear 84# 85#NTP Time DTAI Day Month Year 86# 872272060800 10 # 1 Jan 1972 882287785600 11 # 1 Jul 1972 892303683200 12 # 1 Jan 1973 902335219200 13 # 1 Jan 1974 912366755200 14 # 1 Jan 1975 922398291200 15 # 1 Jan 1976 932429913600 16 # 1 Jan 1977 942461449600 17 # 1 Jan 1978 952492985600 18 # 1 Jan 1979 962524521600 19 # 1 Jan 1980 972571782400 20 # 1 Jul 1981 982603318400 21 # 1 Jul 1982 992634854400 22 # 1 Jul 1983 1002698012800 23 # 1 Jul 1985 1012776982400 24 # 1 Jan 1988 1022840140800 25 # 1 Jan 1990 1032871676800 26 # 1 Jan 1991 1042918937600 27 # 1 Jul 1992 1052950473600 28 # 1 Jul 1993 1062982009600 29 # 1 Jul 1994 1073029443200 30 # 1 Jan 1996 1083076704000 31 # 1 Jul 1997 1093124137600 32 # 1 Jan 1999 1103345062400 33 # 1 Jan 2006 1113439756800 34 # 1 Jan 2009 1123550089600 35 # 1 Jul 2012 1133644697600 36 # 1 Jul 2015 1143692217600 37 # 1 Jan 2017 115# 116# A hash code has been generated to be able to verify the integrity 117# of this file. For more information about using this hash code, 118# please see the readme file in the 'source' directory : 119# https://hpiers.obspm.fr/iers/bul/bulc/ntp/sources/README 120# 121#h 848434d5 570f7ea8 d79ba227 a00fc821 f608e2d4 122